Nonlinear polarization coupling and instabilities in single-mode liquid-cored optical fibers

Polarization coupling is demonstrated in a 0.1-m-long length of nitrobenzene-cored weakly birefringent single-mode optical fiber. Self-switching of the launched mode to the orthogonal polarization is observed at peak powers as low as 1 W. A total phase shift of at least 12pi was induced at a launched peak power of approximately 10 W. To our knowledge, this is the largest phase shift observed experimentally in any nonlinear waveguide at such a low power. The low transmission loss of nitrobenzene makes the device highly attractive for a variety of nonlinear switching applications.